SSAIMS - Stochastic-Selection Ab Initio Multiple Spawning for Efficient Nonadiabatic Molecular Dynamics.

Ab initio multiple spawning provides a powerful and accurate way of describing the excited-state dynamics of molecular systems, whose strength resides in the proper description of coherence effects during nonadiabatic processes thanks to the coupling of trajectory basis functions. However, the simultaneous propagation of a large number of trajectory basis functions can be numerically inconvenient. We propose here an elegant and simple solution to this issue, which consists of (i) detecting uncoupled groups of coupled trajectory basis functions, and (ii) selecting stochastically one of these groups to continue the AIMS dynamics. We show that this procedure can reproduce the results of full AIMS dynamics in cases where the uncoupled groups of TBFs stay uncoupled throughout the dynamics (which is often the case in high dimensional problems). We present and discuss the aforementioned idea in detail and provide simple numerical applications on indole, ethylene and protonated formaldimine, highlighting the potential of stochastic-selection ab initio multiple spawning.